There are severe limitations for conventional scanning electron microscopy of biological material. These include limitations on resolution, lack of back-scattered detection, and the inability to image uncoated, non-conductive samples at low accelerating voltages. All of these capabilities are critically needed by a number of NIH funded investigators and lack of access to them at the University of Arizona is seriously limiting our productivity and progress. As a result, we are requesting funds to purchase a Philips XL30 SEM equipped with a conventional secondary electron detector for optimal detection under high vacuum conditions, and a backscattered electron detector. The Philips XL30 SEM was selected as the instrument on the market having the features which make it the most suitable instrument for the needs of our major user group. These needs include the ability to: (a) obtain high resolution secondary electron images at low voltage on the surfaces of fixed, critical-point dried, but uncoated sample, (c) obtain backscattered electron images of uncoated samples to reveal internal structure as well as the distribution heavy metal (e.g., colloidal gold) labeling of surface structures; (d) record these images in photographic video, or digital format for subsequent presentation, archiving, and/or image analysis. The research plans demonstrate our immediate and critical need for an SEM not only to replace our now defunct, 22 year-old conventional SEM at the College of Medicine Imaging Faculty, but also to provide high-resolution conventional SEM capabilities to eight NIH-funded major users, and at least six NIH-funded minor users in a variety of departments within the University of Arizona and one investigator from the University of Southern California who collaborates with the Principal Investigator for the electron microscopy required for her project.